A horizontal centrifuge for the separation of solids from liquids, e.g. in the dewatering of solids, can comprise a centrifuge drum rotatable about a substantially horizontal axis and having at one axial end, an inlet into which a mixture, slurry or suspension of the solids and the liquid can be introduced for distribution along the cylindrical wall of the centrifuge. This wall, generally referred to as the periphery of the drum, is formed with a multiplicity of openings through which the liquid is expressed by centrifugal force as the drum is rotated with relatively high speeds. A filter cake builds up along the interior of the drum periphery as the solids collect therealong and means can be provided to remove the filter cake at suitable intervals or even continuously if desired. The centrifuge may include means for introducing a washing liquid into the interior of the drum so that this liquid also passes through the filter cake and entrains soluble materials therewith. The inner wall of the drum can be lined with a filter material (filter cloth) defining the mesh size for the filtration process and hence approximately the minimum particle size which can be trapped in the filter cake.
It is known, in order to expedite the filtering operation, to provide a filter drum of such a centrifuge with a filter ring (annular disk) at an end of the centrifuge, generally opposite the inlet for the mixture or suspension. This filter ring, which lies inwardly of the perforated cylindrical wall of the centrifuge drum, is likewise perforated and can be lined with a filtering medium (e.g. the filter cloth) to increase the rate at which the liquid phase is displaced from the drum.
Such systems have been found to be especially effective for the separation of solids from liquids in suspensions (i.e. the dewatering of suspensions). The advantage of such lateral-ring filters is that, when the solids collect rapidly on the filtering surfaces, they tend to impede the throughflow of liquid and, since the centrifugal force drives the solids primarily against the cylindrical wall of the drum, the filter ring remains less obscured and hence permits the rapid draining of liquid from the drum in regions inwardly of the filter cake. As a consequence, a portion of the liquid is not required to traverse the entire thickness of the filter cake in a radial direction. Consequently, such centrifuges have found use wherever a high throughput of liquid is required during the separating operation.
However, they also present certain difficulties, especially when the filter cake is to be washed thoroughly. In such cases, if the washing liquid is permitted to flow predominantly through the side ring, the liquid will not be able to traverse the thickness of the filter cake and the washing will be ineffective. As a practical matter, solvent washing processes cannot be carried out in such drums or with centrifuges embodying same.